The present disclosure relates to a lighting device and a method for manufacturing a lighting device.
An edge-light type backlight is a lighting device that uses a light guide plate, and is designed such that a light-emitting surface of a light-emitting element is disposed facing the lateral surface of the light guide plate. In this backlight, light entering the light guide plate is spread across the entire light guide plate while repeatedly reflecting between a light-extraction surface and a rear surface of the light guide plate. Then, the light exits from the light-extraction surface.
A backlight emitting white light is known to use a blue light-emitting element and to cover the entire light-extraction surface or entire rear surface of the light guide plate with an yellow phosphor layer (a wavelength conversion layer) (see, for example, Japanese unexamined Patent Applications JP 2005-85718 A, JP 2000-009942 A, and JP 2002-096680 A). Part of the blue light emitted from the light-emitting element is wavelength-converted to yellow light with a wavelength conversion layer, and then guided within the light guide plate. The remaining part of the blue light from the light-emitting element is guided within the light guide plate without subjecting wavelength-conversion. In this way, the yellow light and the blue light are mixed together in the light guide plate, thereby producing a white-light backlight.
However, when the entire light-extraction surface or rear surface of the light guide plate is covered with a wavelength conversion layer, some of light propagating in the light guide plate is reflected many times by the light-extraction surface or rear surface covered with the wavelength conversion layer until the light exits from the light guide plate to the outside. Such light will experience wavelength conversion many times, and a part of a blue-light in the white light is further wavelength-converted to yellow light. Thus, light extracted from the light-extraction surface tends to be yellowish white light. In particular, the longer the distance traveled by the light within the light guide plate, the greater the number of reflections of the light at the light-extraction surface or rear surface. Consequently, in light exiting from a position on the light guide plate, the light exiting from the position distant from the light-emitting element has a yellowish color, which might lead to color non-uniformity within a light-extraction region.